A subject-matter of the invention is a fluorinated diol, used in particular for the preparation of a polymer material of polyurethane type for the coating of optical fibre, and its process of preparation.
It is known that optical fibres comprise a double polymer coating composed of a plasticized primary coating in contact with the glass fibre which is topped by a secondary coating. This double coating protects the fibre from mechanical or chemical attacks which can cause attenuation faults for optical transmissions.
Each coating must possess good adhesion to the support which is intended for it and its physical properties must be compatible with the drawing conditions, in particular the drawing rate, and the final use of the fibre. The primary coating must absorb the possible stresses and microbends on the glass. The secondary coating confers, on the fibre, its mechanical properties.
Currently, primary and secondary coatings are coatings of the polyurethane-acrylate type which are photocrosslinked under U.V. radiation.
Application EP-A-0 565 425 discloses a polymer material of fluorinated polyurethane-acrylate type for the coating of optical fibre, which material is based on at least one diol, one diisocyanate and one acrylate, characterized in that at least one of the preceding compounds comprises fluorine and in that at least one of the preceding compounds comprises sulphur.
This material exhibits good mechanical characteristics, in particular an improved static fatigue resistance. However, it uses, for example, a sulphur-comprising diol, which implies high production costs because of the intermediate stage of preparation of the thiol, which results in by-products which have to be removed. The problem is the same with the other sulphur-comprising compounds used for the preparation of the material which is a subject-matter of Application EP-A-0 565 425.
There is thus a search for a material exhibiting the same mechanical properties but which does not involve sulphur-comprising products, in particular which does not involve sulphur-comprising diols.
There is thus a search in particular for a fluorinated diol which does not comprise sulphur.
Thus, the invention provides a fluorinated diol corresponding to the formula (I):
CnF2n+1xe2x80x94Axe2x80x94CH2OCH2xe2x80x94C(CH2OH)2xe2x80x94R
in which n has a value from 2 to 20 and A means xe2x80x94CHxe2x95x90CHxe2x80x94 or xe2x80x94CH2CH2xe2x80x94 and R is an alkyl group comprising 1 to 4 carbon atoms.
According to one embodiment, the fluorinated diol is unsaturated and corresponds to the formula:
CnF2n+1xe2x80x94CHxe2x95x90CHxe2x80x94CH2OCH2xe2x80x94C(CH2OH)2xe2x80x94R.
According to another embodiment, the fluorinated diol is saturated and corresponds to the formula:
CnF2n+1xe2x80x94CH2CH2xe2x80x94CH2OCH2xe2x80x94C(CH2OH)2xe2x80x94R.
According to one embodiment, in the formula (I), R is C2H5.
According to one embodiment, in the formula (I), n is an integer and is between 6 and 14 inclusive.
According to one embodiment, in the formula (I), CnF2n+1 results from a mixture and n is between 6 and 14 inclusive.
According to one embodiment, in the formula (I), n is between 6 and 8 inclusive.
The invention also provides a process for the preparation of a fluorinated diol according to the invention, when the latter is unsaturated, comprising the radical reaction of CnF2n+1I with the trimethylolalkane monoallyl ether, the alkane corresponding to the R group augmented by one carbon atom, and then the dehydroiodination.
The invention also provides a process for the preparation of a fluorinated diol according to the invention, when the latter is saturated, comprising the radical reaction of CnF2n+1I with the trimethylolalkane monoallyl ether, the alkane corresponding to the R group augmented by one carbon atom, and then the direct reduction.
The invention also provides a process for the preparation of a fluorinated diol according to the invention, when the latter is saturated, comprising the radical reaction of CnF2n+1I with the trimethylolalkane monoallyl ether, the alkane corresponding to the R group augmented by one carbon atom, and then the hydrogenolysis.
The invention also provides a process for the preparation of a fluorinated diol according to the invention, when the latter is saturated, comprising the radical reaction of CnF2n+1I with the trimethylolalkane monoallyl ether, the alkane corresponding to the R group augmented by one carbon atom, then the dehydroiodination and then the hydrogenation.
The fluorinated diol according to the invention is in particular devoid of sulphur.
The diisocyanates and the compounds comprising ethylenic unsaturation, such as vinyl ethers and acrylates, are the compounds conventionally used in the field under consideration. These compounds may or may not be fluorinated. The diisocyanate might be replaced by a polyisocyanate but, for the purposes of convenience, it is the first term which is used generically. Examples of such diisocyanate, acrylate and vinyl ether compounds can be found, for example, among the compounds mentioned in Application EP-A-0 565 425 and Application FR-A-2 712 291.
For the preparation of the coatings of fibres, the material according to the invention, which exhibits, inter alia, the distinguishing feature of being crosslinkable, is photocrosslinked, generally by U.V. radiation, preferably in the presence of a reactive diluent, generally a diacrylate, present in a conventional amount.
Use is conventionally made of photoinitiators and/or catalysts for (photo)chemical reactions, if required.
The fluorinated diols used in the invention are novel.
The fluorinated diols of the invention in which R is C2H5 are prepared by radical reaction of CnF2n+1I with allyloxytrimethylolpropane (or trimethylolpropane monoallyl ether), followed either by a dehydroiodination, optionally followed by a hydrogenation, or by a direct reduction or by a hydrogenolysis.
As the description is given with reference to the diol in which R is C2H5, it is clear that the other compounds are prepared in the same way starting from the appropriate monoallyl ether. This monoallyl ether is the trimethylolalkane monoallyl ether, the alkane corresponding to the R group augmented by one carbon atom.
The radical addition can be carried out according to well known procedures, either in bulk or in an organic solvent or in water.
Such a radical addition is disclosed in Patent Application DE-A-2 336 913, the reaction conditions of which may be followed.
Use may be made, as organic solvent, of acetone, tetrahydrofuran, dioxane, dimethylformamide, N-methyl-2-pyrrolidone, dimethyl sulphoxide, methyl ethyl ketone, methyl isobutyl ketone, ethanol, isopropanol and isopropyl acetate. Use will preferably be made of a water-soluble solvent or a mixture of water-soluble solvents.
The radical addition is generally carried out in the presence of (an) initiator(s) which is/are used in the proportion of 0.1 to 1.5% with respect to the total weight of the monomers charged, preferably 0.1 to 0.5%. Use may be made, as initiators, of peroxides, such as, for example, benzoyl peroxide, lauroyl peroxide, succinyl peroxide and tert-butyl perpivalate, or azo compounds, such as 2,2xe2x80x2-azobisisobutyronitrile, 4,4xe2x80x2-azobis(4-cyanopentanoic acid) and 2,2xe2x80x2-azobis(2-methylbutanenitrile).
The reaction temperature can vary within wide limits, that is to say between ambient temperature and the boiling point of the reaction mixture. The reaction is preferably carried out between 60 and 90xc2x0 C. (the formation of polymers is thus avoided). With the same aim, it is possible to carry out the reaction by running in allyloxytrimethylolpropane, which makes it possible to control the reaction and to limit the rise in temperature.
An iodinated addition product is thus obtained.
The dehydroiodination is carried out using a strong inorganic base, such as sodium hydroxide or potassium hydroxide, or a strong organic base, such as DBU (1,8-diazabicyclo[5.4.0]undec-7-ene). The reaction is preferably carried out in an aqueous medium. The amount of strong base used is, for example, in the region of stoichiometry. The temperature is generally restricted to approximately 70-75xc2x0 C. (the formation of polymers is thus avoided).
An unsaturated diol is thus obtained.
The saturated diols can be produced according to various methods. They can be obtained from the iodinated addition product by hydrogenolysis in the presence of an alkaline agent or else by reduction with sodium borohydride or zinc borohydride or lithium aluminium hydride or tributyltin hydride. They can also be obtained from the unsaturated derivative by catalytic hydrogenation according to known methods, without solvent or else in solution in a conventional organic solvent, such as ethanol or methanol, in the presence of a hydrogenation catalyst which can, depending upon the situation, be either Raney nickel or palladium-on-charcoal.
A saturated diol is thus obtained.
The perfluoroalkyl group CnF2n+1 can be linear or branched. The compound CnF2n+1I is known per se and is prepared by conventional processes.